LOS ANGELES » Talk about a triple threat. If you thought tyrannosaurs weren’t scary enough, try three of them at the same time. Turns out these fearsome beasts weren’t solitary hunters — they ran in gangs, according to a study of the first fossil tyrannosaurid trackways ever discovered.

The three sets of fossil footprints, described in a PLOS One paper called "A Terror of Tyrannosaurs," show clear evidence that these animals were "gregarious": They operated in packs rather than alone, as once thought.

While paleontologists have dug up a decent number of tyrannosaur bones, their footprints have been few and far between, according to the study led by Richard McCrea, a researcher at Peace Region Palaeontology Research Center. Those few that have been found are single, solitary footprints, not part of a trail. And that’s too bad, because a series of footprints (referred to as "trackways") can reveal certain things that bones alone may not, including the animal’s gait, how fast it could go and who it was traveling with at the time.

But in October 2011, Aaron Fredlund, a local guide-outfitter, found the first two prints of the animal’s trackway in northeastern British Columbia, and the remaining prints were later uncovered by researchers and volunteers. The trackways were named in honor of the man who discovered the first prints: Bellatoripes fredlundi. (Bellatorius is Latin for "warlike," an homage to these terrifying predators.)

The high clay content of the squishy ground the dinosaurs walked through is probably what helped preserve the footprint impressions so well, the authors said. The clay even preserved imprints of the "tubercles" on the animals’ rough skin.

The footprints, which stretch longer than 19.5 inches, are all pointed in the same direction, headed southeast, and are within 8.5 meters of each other. Since these large predators were typically few and far between on the landscape — "only five percent of the faunal composition," the authors write — it’s highly unlikely that three solitary tyrannosaurs just happened to be in the same place at the same time walking in parallel.

By analyzing the gait of each animal from one footprint to the next, the scientists think the animals were traveling around 3.9 to 5.3 mph.

The researchers aren’t sure what kind of tyrannosaur these carnivores were — there were a number of different species in the region, including Albertosaurus, Gorgosaurus and Daspletosaurus.

But regardless, these first-of-their-kind findings shed new light on how these long-gone hunters once moved and behaved.